I think you are over confident about 2FA. If an attacker personally knows you and knows that you control a large amount of bitcoin the they could steal your 2FA device and guess your simple password.
IMO a 2FA device should supplement your password not replace it
IMO a 2FA device should supplement your password not replace it
The phone I'd do this on would get airplane mode enabled when it's first turned on, then the phone itself would be encrypted with a strong password. I don't know if you're familiar with Android's phone encryption, but you have to enter a password just to decrypt the phone itself before getting to the lock-screen, where you'd have to enter another combination. That'd be pretty hard to get pass.
I agree with 2FA being a supplement and not a replacement.
Yes.. But really how likely of a scenario is this / what can be done about it? And for the second two scenarios you mentioned, its as easy as not letting someone borrow it for a phone call and not letting someone easily watch over your shoulder as you put your password in.
I think its a good idea. There may be vulnerabilities, there usually are, I guess its all about acceptable risk.